Development of Continuous-Wave Terahertz Lasers

本研究旨在发展基于多量子阱（MQW）结构子带间跃迁的连续波（CW）固态太赫兹激光器。如果成功实施，该项目将对THz（1-10 THz）或远红外光谱的科学和技术产生重大影响，目前还没有以CW模式工作的相干和强固体源。为了实现这一目标，已经进行了广泛的研究子带间跃迁，散射和磁隧道光谱的辐射特性;模拟辅助设计合适的多量子阱;和光谱分辨测量太赫兹自发辐射从多量子阱。详细的分析表明，在合理的粒子数反转密度为2 '109/cm ~ 2时，可以实现电泵浦激光。这项为期三年的计划拟于二○ ○二年八月一日展开。第一年将集中在两个并行的任务：提高成品率在一种新型的金属波导结构的太赫兹模式限制，和几个有前途的MQW结构的调查制造。金属波导结构在实现连续激光器操作方面将在两个重要方面非常有用，即降低激光阈值，从而降低功率耗散和改善散热。制造过程包括晶片键合和选择性蚀刻，它已经在主要研究者的小组中开发出来。有前途的多量子阱结构包括使用电子-LO-声子散射的结构，用于减少较低的激光能级，使用电子-电子散射的结构，和啁啾超晶格结构，其中的辐射跃迁是发生在两个微带之间。这些多量子阱结构的设计将通过复杂的计算机模拟来辅助，包括用于输运分析的蒙特卡罗模拟。根据这项调查的结果，第二年和第三年将集中在最有前途的结构和提高粒子数反转的鲁棒性，以实现连续激光操作。还将努力开发单模和频率稳定的太赫兹激光器，用于太赫兹外差接收器中的本机振荡器应用。

The proposed research seeks to develop continuous-wave (CW) solid-state THz lasers based on intersubband transition in multiple quantum-well (MQW) structures. If carried out successfully, this project will have a major impact on the science and technology of the THz (1-10 THz) or far-infrared spectrum, where currently no coherent and intense solid-sate sources operating in the CW mode are available. Towards this goal, extensive studies have already been performed on the radiation properties of intersubband transition, scattering, and magneto-tunneling spectroscopy; the simulation-aided design of suitable MQWs; and spectrally resolved measurements of THz spontaneous emissions from MQWs. Detailed analysis indicates that electrically pumped lasing can be achieved at a reasonable population inversion density of 2'109/cm2. A three-year project is proposed to start on August 1, 2002. The first year will focus on two parallel tasks: improvement of the yield rate in fabrication of a novel metal waveguide structure for THz mode confinement, and investigation of several promising MQW structures. The metal waveguide structure will be very useful in achieving CW laser operation in two important ways, reducing the lasing threshold and thus the power dissipation and improving heat removal. The fabrication process involves wafer bonding and selective etching, and it has already been developed in the principal investigator's group. The promising MQW structures include a structure using electron-LO-phonon scattering for depopulation of the lower lasing level, a structure using electron-electron scattering for depopulation, and a chirped superlattice structure in which the radiative transition is to take place between two minibands. The design of these MQW structures will be aided by sophisticated computer simulations, including Monte Carlo simulation for transport analysis. Based on the results from this investigation, the second and third years will focus on the most promising structure and on the improvement of robustness of population inversion, in order to achieve CW lasing operations. Efforts will also be made to develop single-mode and frequency-stabilized THz lasers for local-oscillator applications in THz heterodyne receivers.